Introduction to C++ Introduction to C++ 1

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2 What Is C++? (Mostly) an extension of C to include: Classes Templates Inheritance and Multiple Inheritance Function and Operator Overloading New (and better) Standard Library References and Reference Parameters Default Arguments Inline Functions Note: Objective C was invented at about the same time, with similar goals. A few small syntactic differences from C 2

3 Compiling C++ Use gcc, Visual Studio, etc. File types.cc,.cp,.cpp,.cpp,.cxx,.c++,.c.h,.h Some of these have special properties. 3

4 Background C++ was developed by Bjarne Stroustrup at Bell Laboratories Originally called C with classes The name C++ is based on C s increment operator (++) Indicating that C++ is an enhanced version of C Widely used in many applications and fields Well-suited to Programming in the Large 4

5 A Simple C++ Example // C++ simple example C++ style comments #include <iostream> //for C++ Input and Output int main () { standard output stream object int number3; stream insertion operator std::cout << "Enter a number:"; std::cin >> number3; int number2, sum; stream extraction operator standard input stream object std::cout << "Enter another number:"; std::cin >> number2; sum = number2 + number3; std::cout << "Sum is: " << sum <<std::endl; } return 0; stream manipulator Concatenating insertion operators 5

6 A Simple C++ Program <iostream> Must be included for any program that outputs data to the screen or inputs data from the keyboard using C++ style stream input/output. Replaces <stdio.h> of C C++ requires you to specify the return type, possibly void, for all functions. Specifying a parameter list with empty parentheses is equivalent to specifying a void parameter list in C. 6

7 18.5 Header Files C++ Standard Library header files Each contains a portion of the Standard Library. Function prototypes for the related functions Definitions of various class types and functions Constants needed by those functions Instruct the compiler on how to interface with library and user-written components. Header file names ending in.h Are old-style header files Superseded by the C++ Standard Library header files Use #include directive to include class in a program. 7

8 Fig C++ Standard Library header files C++ Standard Library header files <iostream> <iomanip> <cmath> <cstdlib> <ctime> <vector>, <list> <deque>, <queue>, <stack>, <map>, <set>, <bitset> Explanation Contains function prototypes for the C++ standard input and standard output functions. This header file replaces header file <iostream.h>. This header is discussed in detail in Chapter 26, Stream Input/Output. Contains function prototypes for stream manipulators that format streams of data. This header file replaces header file <iomanip.h>. This header is used in Chapter 26, Stream Input/Output. Contains function prototypes for math library functions. This header file replaces header file <math.h>. Contains function prototypes for conversions of numbers to text, text to numbers, memory allocation, random numbers and various other utility functions. This header file replaces header file <stdlib>. Contains function prototypes and types for manipulating the time and date. This header file replaces header file <time.h>. These header files contain classes that implement the C++ Standard Library containers. Containers store data during a program s execution. 8 Continues for three pages!

9 Needed for Lab #4 <iostream> cin and cout for stream input and output <cmath> sqrt() 9

10 References in C++ Definition Reference: An Alternative Name for an Object BIG difference from Java References are only created in declarations and parameters A reference can only appear where the object itself could have appeared 14

11 Simple References void f() { int j = 1; int &r = j; int x = r; // x now is 1 r = 2; // j now is 2 } //f //r and j refer to same int Sometimes, reference declarations are written as int& r1 = k int k; int &r1 = k; // okay: r1 is initialized int &r2; extern int &r3;//okay; r3 defined elsewhere // error; initializer missing 15

12 Simple References (continued) void g() { int ii = 0; int &rr = ii; rr++; //ii now is 1 These '*' and '&' are not operators but rather declaration qualifiers. This '&' is the unary address operator brought over from C. int *pp = &rr; } //g // pp now points to ii Note: This declares a pointer exactly as in C, and initializes it with the address of rr (which is another name for ii) 16

13 Example Usage of a Reference int grid[1000]; int rowsize, x, y;... int &element = grid[x*rowsize+y];... /* computations on integer named element */ 17

14 Reference Parameters An alias for its corresponding argument in a function call. & placed after the parameter type in the function prototype and function header Example int &count in a function header Pronounced as count is a reference to an int Parameter name in the called function body actually refers to the original variable in the calling function. 18

15 Reference Parameter Example C version void swap (int *a, int *b) { int temp = *a; *a = *b; *b = temp; } // void swap( ) Hazard: a NULL pointer C++ version void swap (int &a, int &b) { int temp = a; a = b; b = temp; } // void swap( ) Non-hazard: no pointer here 19

16 Notes on References and Pointers Pointers in C do multiple duty Links, as in linked lists and trees Parameters, where the function needs to return a value to an argument provided by the caller Short-hand, a short way of referring to an object that otherwise would need a complex expression 20

17 Java vs. C++ References In Java, a reference is a data type. It can be assigned to, compared, copied, stored, etc. Same reference can refer to different objects at different times during execution In C++, a reference is an alias for an object It cannot be assigned to; assignment is through the reference to the underlying object Similar to dereferencing a pointer in C A reference always refers to the same object for the duration of its scope 21

18 Repeat Three Times A reference is not a pointer, A reference is not a pointer, A reference is not a pointer, And neither of them resembles a Java reference 22